This invention relates to a sine wave generator using digital circuitry to provide variable encoding in the simulation of sine waves of differing frequency.
The generation of simulated sine waves from digital data is a well-known technique for converting digital information to analog form. The circuit arrangements are relatively complex designs and typically include a network of resistors and switches to achieve a piece-wise approximation of a sine wave. The frequency of the generated signal and the number of segments used in the encoding of each cycle of the signal determine the rate at which the encoding switching takes place. The achieving of reliable switching operation at frequencies in the range of 100 MHz is difficult and often imposes a limitation on the encoding scheme used to generate the sine wave.
The generation of simulated sine waves of different frequencies in accordance with received digital data is important in the networking of computer equipment. The ability of multiple computers to be interconnected in a network enables the computers to communicate with shared equipment such as file servers as well as other computer stations. One method of successfully linking individual computers to a network converts the data into analog signals for transmission through cable extending therebetween.
The data in digital form is converted to analog form by encoding a sine waveform and varying the frequency in accordance with the transmitted data. A number of different encoding patterns have been utilized. However, the use of a single encoding system to simulate wave forms of different frequencies from digital data signals can introduce problems in the decoding of the signals. While the encoding of a high frequency signal can be accomplished with a reduced number of segments when compared with a low frequency signal having a longer period without making the signal unrecognizable, the use of the same number of segments to simulate the low frequency signals may end up producing an unacceptable waveform. Furthermore, the short period of the high frequency signal can only accommodate a limited number of switching operations in that interval and that limited number may not be sufficient to create a useful approximation to the longer period, low frequency signal. The effects of the less than satisfactory representation of the lower frequency signal are compounded by distortion and losses resulting from the switches, the transmission line and the subsequent circuitry. The problem is exacerbated by the high rates of data transmission used in networks. As a result, the potential for loss of transmitted data increases when a single encoding pattern is used for the different frequency analog signals.
Accordingly, the present invention is directed to the provision of a sine wave generator using digital circuitry to generate analog signals of differing frequency in response to a data stream. In addition, the subject invention is intended for use with high rate data streams without requiring the operation of switching devices at multiples of the data rate. Further, the system employs variable encoding for the generation of wave forms at different frequencies thereby providing a readily recognizable representation of the desired sine wave form.